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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/45409

Title: Characteristics of gas hydrate and free gas offshore southwestern Taiwan from a combined MCS/OBS analysis
Authors: P. Schnurle;C.-S. Liu;T.-H. Hsiuan;T.-K. Wang
Contributors: 國立臺灣海洋大學:應用地球科學研究所
Keywords: amplitude versus angle analysis;gas hydrate and free gas;reflection–refraction seismic;southwestern Taiwan
Date: 2004-03
Issue Date: 2018-03-16T08:13:51Z
Publisher: Marine Geophysical Researches
Abstract: Abstract:In this study, we present the results of the combined analyses of ocean bottom seismometer and multi-channel seismic reflection data collection offshore southwestern Taiwan, with respect to the presence of gas hydrates and free gas within the accretionary wedge sediments. Estimates of the compressional velocities along EW9509-33 seismic reflection profile are obtained by a series of pre-stack depth migrations in a layer stripping streamlined Deregowski loop. Strong BSR is imaged over most of the reflection profile while low velocity zones are imaged below BSR at several locations. Amplitude versus angle analysis that are performed within the pre-stack depth migration processes reveal strong negative P-impedance near the bottom of the hydrate stability zone, commonly underlain by sharp positive P impedance layers associated with negative pseudo-Poisson attribute areas, indicating the presence of free gas below the BSR. Ray tracing of the acoustic arrivals with a model derived from the migration velocities generally fits the vertical and hydrophone records of the four ocean-bottom seismographs (OBS). In order to estimate the Poisson’s ratios in the shallow sediments at the vicinity of the OBSs, we analyze the mode-converted arrivals in the wide-angle horizontal component. P-S mode converted reflections are dominant, while upward P-S transmissions are observed at large offsets. We observe significant compressional velocity and Poisson’s ratio pull-down in the sediment below the BSR likely to bear free gas. When compared to Poisson’s ratio predicted by mechanical models, the values proposed for the OBSs yield rough estimates of gas hydrate saturation in the range of 0–10% in the layers above the BSR and of free gas saturation in the range of 0–2% just below the BSR.
Relation: 25 pp.157-180
URI: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/45409
Appears in Collections:[應用地球科學研究所] 期刊論文

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